Light intensity explained

Several measures of light are commonly known as intensity:

• Radiant intensity, a radiometric quantity measured in watts per steradian (W/sr)
• Luminous intensity, a photometric quantity measured in lumens per steradian (lm/sr), or candela (cd)
• Irradiance, a radiometric quantity, measured in watts per square meter (W/m²)
  • Intensity (physics), the name for irradiance used in other branches of physics (W/m²)
• Radiance, commonly called "intensity" in astronomy and astrophysics (W·sr⁻¹·m⁻²)

See also

• Brightness, the subjective perception elicited by the luminance of a source
• Luminance, the photometric equivalent of radiance (lm·sr⁻¹·m⁻²)
• Photometry (optics), measurement of light, in terms of its perceived brightness to the human eye
• Radiometry, measurement of light, in absolute power units